Kung Pow: Enter the First was far and away the most awful movie I've ever seen. It's acceptable when a joke isn't funny, since comedy is often a volume business. But it's bad when an unfunny joke goes on for way too long (like the 'Pussies, Dicks, and Assholes' speech from Team America), but it's absolutely inexcusable when that joke gets repeated (see above). Kung Pow was nothing but that.
I love comedy and feel that I have a strong outsiders perspective (meaning that I'm not a comic myself, although I've been on stage). Conan O'Brien is known for doing many jokes that are funny, but you don't know why (The masturbating bear is an example). Kung Pow mostly consisted of jokes that not only weren't funny, but you didn't understand why they were SUPPOSED to be funny. Like when Master Pain changes his name to Betty. It's a sudden joke that they don't go into later. The mere act of changing the male antagonists' name to a female one isn't funny without any sort of context. It would be like someone from Monty Python sitting in the middle of the stage wearing a dress. I don't mean with some underlying context, I mean just sitting there, no script, no movement, no outside activity.
Kung Pow is my go-to movie when anyone asks what the worst movie I've ever seen is.
PS. Cats and Dogs was crap, too. I was suckered by the trailer when I saw the dog say 'Son of my mom!' I thought that was a hilarious line that allowed for adult humour in a kids movie (kind of like Animaniacs doing an episode based on 'Apocalypse Now'). But it was a tease, it was the only funny line in the whole movie (which, by itself, puts it over Kung Pow). And the worst sin of all is that it completely wasted the voice-over talents of Jon Lovitz. Lovitz was hilarious in The Critic and has an outstanding singing voice. And they did absolutely nothing with him. Sean Hayes wasn't given that much to do either.
PPS. A lot of people are listing movies that are so bad, they're funny. Movies like Riki-Oh and Troll 2. My two movies are genuinely terribly and unfunny in any way. Also, Fight Club and Superbad? Come on, now....